EP1538514B1 - Transparent substrate with invisible electrodes and devices incorporating the same - Google Patents

Abstract

A transparent substrate comprises invisible electrodes including a transparent support having transparent conductive film. The electrodes and their contact zones are structured with contours separated by non-conductive spaces, where the conductive film located at the site of the non-conductive spaces includes nano fissures. A transparent substrate comprises invisible electrodes including a transparent support having transparent conductive film, where electrodes and their contact zones are structured with contours separated by non-conductive spaces, where the conductive film located at the site of the non-conductive spaces includes nano fissures for interrupting the electrical conductivity between neighboring electrodes, without altering the path of a light ray in a manner perceptible to the naked eye. An independent claim is also included for a method of manufacturing a transparent substrate, comprising: (1) placing the substrate, formed of the support and the conductive film possibly deposited on an intermediate layer made of a transparent hard non-conductive material, in a sealed enclosed space having a gaseous fluid supply inlet and a pump outlet; (2) inserting, between the UV radiation source and the substrate, a mask including windows transparent to UV radiation, the windows corresponding to the dielectric non-conductors; and (3) adjusting, as a function of the choice of materials used for the substrate and the emitting source, the UV radiation features to cause nano fissures to be created in the conductive film in the radiated zone, without removing any matter.

Description

The present invention relates to a transparent substrate having at least one face provided with transparent electrodes whose structure is such that their contours can not be perceived by an observer in the wavelength range of visible light.

The invention also relates to devices, generally electronic devices, comprising one or more transparent substrates with invisible electrodes in which the electrodes have control or energy collector roles, and more particularly such devices arranged above the electrodes. display of an electronic device on which the information of said display must be read without being hindered by the structuring and the arrangement of the electrodes.

The invention also relates to a method for performing, economically and with high precision, structuring of the electrodes on any transparent substrate while providing optical compensation between the electrodes to make their contours invisible.

Solutions have already been proposed so that the interface formed by electrodes arranged between a display and an observer remains as discrete as possible and does not harm the aesthetic appearance of the electronic device, particularly in the case of a room. watchmaking. For example, wristwatches are known whose inner face of the ice includes electrodes allowing a tactile control of the hourly or non-hourly functions by capacitive or resistive effect, as is described in a non-limiting manner in the US Patents 4,228,534 , EP 0 674 247 and EP 1 207 439 . The ice can also be replaced or supplemented by a cell formed of two substrates with transparent electrodes between which is placed an active material, for example to form a photovoltaic cell constituting the energy source as described in document WO 93/19479 , or to form a liquid crystal cell which may have a transparent state and a state to display on request additional or different information from that displayed on an underlying dial, as described in the document WO 99/32945 .

To achieve the electrodes transparent conductive oxides (TCO) are used in known manner, that is to say materials which are both good conductors and transparent in the visible, such as tin oxide and indium (ITO), In ₂ O ₃ or SnO ₂ doped with antimony. It can also be used as a conductive film for structuring electrodes of transparent conductive polymers which are conjugated double bond organic compounds whose conductivity can be enhanced by chemical or electrochemical doping. It is for example a polyacetylene or polyanilines such as Ormecon®. These deposits, of the order of 50 to 100 nm, are made directly on the transparent substrate or on an intermediate layer by a large number of known techniques such as spraying, evaporation, sol-gel technique, and techniques. of vapor deposition (CVD), which will particularly note laser assisted deposition (LICVD).

As regards the structuring of the electrodes, there are also various known methods used, using at least one mask corresponding to the electrode contour, or during the deposition of the TCO by localized crystallization of a sol-gel film by irradiation with a UV laser, either by performing a chemical etching on a continuous TCO film, or a localized ablation by irradiating with a UV laser at a sufficient fluence or mechanical ablation, as described in FIG. US Patent 6,225,577 . The nature of the transparent substrate, glass or plastic, is obviously decisive from the technical and economic point of view for the choice of the process to be applied. Localized crystallization of a sol-gel film by UV laser is, for example, hardly applicable to a plastic substrate, such as PMMA, because it is a photothermal process.

On the other hand, the use of very aggressive chemical compounds in selective etching processes can lead to a degradation of the substrate or an intermediate layer interposed between said substrate and the TCO film, such as non-conductive spaces between the electrodes can still remain perceptible to the naked eye, regardless of how to fill said non-conductive spaces. These non-conductive spaces may also be visible because of the difficulty of filling them without forming beads or depressions capable of deflecting the light rays, since it is necessary to use two complementary masks, respectively for etching and for the lining.

To overcome the aforementioned drawback, the method proposed in the application European EP 1 457 865 , in the name of the applicant, consists in using a single mask by employing laser radiation whose characteristics (fluence, number of pulses, frequency) are adjusted in two different modes for two successive steps. The first step is to completely eliminate the TCO in the non-conductive spaces, and the second step to cause the deposition of a material of refractive index and thickness appropriate in said spaces. It seemed rather obvious that two close electrodes from each other could only be electrically isolated by removing all traces of conductive material in the space between them.

Surprisingly, however, it appeared that the electrical conductivity could be lowered to such a low level that two adjacent electrodes were electrically isolated, without however eliminating the TCO, which makes it possible to maintain the initial optical properties, and thus to make the contours invisible. electrodes, regardless of the angle under which there is a transparent substrate having said electrodes.

To this end, the subject of the invention is a transparent substrate with invisible electrodes comprising a transparent support on which is deposited a transparent conductive film in which electrodes are structured with contours separated by non-conductive spaces. The substrate is characterized in that the conductive film at the location of said non-conductive spaces comprises nanofissures, the greater number of which crosses the entire thickness of the conductive film, making it possible to interrupt the electrical conductivity between adjacent electrodes, without modifying the path of a ray of light in a manner noticeable to the naked eye. The edges of these nanofissures are at most separated by a few microns and can not be seen by an observer whose visual acuity does not allow him to distinguish, in close vision (20 - 30 cm), objects distant from less than 1 / 10 millimeters.

The conductive film may be a transparent conductive oxide (TCO), but also a transparent conductive polymer. However, in the remainder of the description, reference will be made essentially to TCOs, which are the most known products for producing transparent electrodes.

In a preferred embodiment, prior to the deposition of the TCO film, the transparent support is coated with a layer of hard non-conductive hard material (Hard coating) which contributes to the formation of nanofissures.

According to another preferred embodiment, after the structuring of the electrodes, the entire surface of the substrate, that is to say the electrodes and the non-conductive spaces, with the possible exception of the contact zones of the electrodes, is covered with a protective film, which can also have anti-reflection properties and helps stabilize the nanofissures over time.

• placer le substrat, formé du support et du film de TCO éventuellement déposé sur une couche intermédiaire, dans une enceinte fermée ayant une amenée de fluide gazeux et une sortie de pompage;
• interposer, entre la source de rayonnement UV et le substrat, un masque comportant des fenêtres transparentes au rayonnement UV, lesdites fenêtres reproduisant les contours désirés des espaces non conducteurs, et
• en fonction des matériaux utilisés pour former le substrat, de leurs épaisseurs et du choix de la source émettrice, ajuster les caractéristiques du rayonnement pour provoquer une nanofissuration du film de TCO sans enlèvement de matière.

The nanofissures in the TCO layer are obtained by UV irradiation using a laser source. For this, the method consists of:

• placing the substrate, formed of the support and the TCO film optionally deposited on an intermediate layer, in a closed chamber having a gaseous fluid supply and a pumping outlet;
• interposing, between the UV radiation source and the substrate, a mask having windows transparent to UV radiation, said windows reproducing the desired contours of the non-conductive spaces, and
• depending on the materials used to form the substrate, their thickness and the choice of the emitting source, adjust the characteristics of the radiation to cause nanofissuration of the TCO film without removal of material.

As regards the choice of the source, a pulsed excimer laser which emits mainly in the ultraviolet light and whose use is known to carry out photoablation or marking is preferably used. It is, for example, a short-pulse (20 ns) KrF (λ = 248 nm) excimer or a long-pulse (250 ns) XeF (λ = 308 nm) excimer. By "radiation characteristics" is meant the fluence, the number of pulses and their frequency.

The adjustment of these characteristics must take place between a lower limit where cracks can be observed, but without a sufficient decrease in the electrical conductivity, and an upper limit causing the removal of the TCO layer making the contours of the electrodes visible, since the usual insulating space between the electrodes is of the order of a few tenths of a millimeter. It is obviously possible, as indicated in the application No 03005615.4 already cited, to fill these spaces with a transparent dielectric material to obtain an optical compensation.

The method according to the invention therefore has the advantage of not requiring the above step, and therefore of being more economical. Nor does it impose the delicate choice of a dielectric material having a refractive index and a thickness adapted to obtain a satisfactory optical compensation, given the specific characteristics of the TCO film (refractive index and thickness).

After structuring the electrodes, it may be advantageous to leave the substrate in the enclosure, to replace the previous mask with another mask whose UV-transparent window makes it possible to deposit a transparent protective film on the entire substrate. , that is to say the electrodes and the non-conductive spaces, with the possible exception of the contact areas of the electrodes, by introducing a precursor gas into the chamber. To form the protective film, a material is preferably chosen whose nature and thickness make it possible to have anti-reflection properties. The film also has the advantage of stabilizing nanofissures over time.

Thus, a transparent substrate with invisible electrodes is usable in all the applications mentioned in the preamble by offering qualities of transparency and uniformity superior to those of the known products of the prior art.

• la figure 1 est une représentation schématique d'un dispositif permettant d'obtenir un substrat transparent à électrodes invisibles selon l'invention;
• les figures 2 et 3 représentent les étapes de fabrication d'un premier mode de réalisation;
• les figures 4, 5 et 6 représentent les étapes de fabrication d'un deuxième mode de réalisation;
• la figure 7 représente le schéma de montage permettant d'effectuer des mesures électriques;
• la figure 8 est une vue d'une zone diélectrique nanofissurée selon l'invention;
• la figure 9 correspond à la figure 8 lorsque les caractéristiques du rayonnement UV sont insuffisantes;
• la figure 10 correspond à la figure 8 lorsque les caractéristiques du rayonnement UV sont au contraire excessives, et
• la figure 11 est une image AFM d'une nanofissure référencée à la figure 8.

Other characteristics and advantages of the present invention will appear in the following description, given by way of illustration and without limitation, with reference to the appended drawings in which:

• the figure 1 is a schematic representation of a device for obtaining a transparent substrate with invisible electrodes according to the invention;
• the Figures 2 and 3 represent the manufacturing steps of a first embodiment;
• the Figures 4, 5 and 6 represent the manufacturing steps of a second embodiment;
• the figure 7 represents the circuit diagram for performing electrical measurements;
• the figure 8 is a view of a nanofissured dielectric zone according to the invention;
• the figure 9 corresponds to the figure 8 when the characteristics of UV radiation are insufficient;
• the figure 10 corresponds to the figure 8 when the characteristics of the UV radiation are on the contrary excessive, and
• the figure 11 is an AFM image of a nanofissure referenced to the figure 8 .

The figure 1 schematically represents the device which basically comprises a source 14 of UV radiation constituted by a laser source, a telescope type optical comprising a converging lens 16 and a diverging lens 18 making it possible to reduce the section of the laser beam in order to increase its fluence, a mask 10 comprising zones 12 transparent to UV radiation, and an enclosure 2. The enclosure 2 comprises a window 8 transparent to UV radiation, a gas supply 4 and a pumping outlet 6. The chamber 2 may also include an additional supply (not shown) of a carrier gas of a precursor gas. Inside the chamber 2 is placed a substrate which, in this example, has a transparent base which is already coated with a TCO film. It would obviously be possible to form the TCO film directly in the enclosure 2, for example by LICVD, but of less economic interest, since the energy consumption would be 100 times greater.

The UV radiation source is an eximeric laser, such as a long pulse (250 ns) XeF laser (308 nm) providing maximum energy 150 mJ per pulse with a 1.9 x 2.4 cm ² rectangular beam, or a short pulse (20 ns) KrF (248 nm) laser providing a maximum energy of 180 mJ per pulse with a rectangular beam of 1 , 5 x 4 cm ² . Other lasers, for example a tripled or quadrupled Nd: YAG laser, can of course be used, provided that the characteristics are adjusted to the desired objective.

The Figures 2 and 3 correspond to the simplest embodiment in which a support 1 of a transparent material is coated with a continuous film of TCO, such as a tin oxide and indium (ITO) having in this example a thickness of 70 nm. It would obviously be possible to use another TCO, such as In ₂ O ₃ or Sn O ₂ doped with Sb, and to have a different thickness, for example between 50 and 100 nm, preferably between 65 and 75 nm. As represented in figure 3 after UV irradiation in the chamber 2, non-conductive spaces 9 created by nanofissures 11 passing through the ITO film and electrically separating the electrodes 7 and the contact zones 15 are formed. To obtain these cracks and not the ablation of the ITO in these electrical spaces 9, it is necessary to adjust the characteristics of the UV radiation in such limits that the depth of the nanofissures causes an interruption of the conductivity sufficient to electrically isolate neighboring electrodes, without however causing a removal of the ITO layer, as explained in more detail for the second embodiment corresponding to the Figures 4 to 6 .

To the figure 4 it can be seen that the substrate consists of a support 1, which is in this example PMMA, on which is deposited an intermediate layer 3 made of a non-conductive hard hard material (hardcoating). This intermediate layer, which protects the PMMA and which contributes to stabilize the base of the ITO after nanofissuration, is for example composed of a resin incorporating SiO ₂ and its thickness is of the order of 20 microns. This substrate is placed in the chamber 2, then subjected through the mask 10 to the UV radiation of a source 14. In the examples which follow, the source is constituted by a XeF eximer laser (λ = 308 nm) to long pulses (250ns), with as 20-pulse illumination characteristics at 5 Hz with an illuminated surface of 3 x 4 mm ² , by varying the fluence.

The figure 5 schematically represents the formation of nanofissures 11 creating the non-conductive spaces 9 separating the electrodes 7 and the contact zones 15.

The figure 6 represents an optional step in which the substrate remains in the chamber 2, but where the mask 10 has been replaced by another mask whose radiation-transparent window delimits the useful contour of the transparent substrate. A precursor gas is then introduced into the chamber via the supply duct 4, which makes it possible to deposit a protective film 13 by performing a new adjustment of the characteristics of the UV radiation. The film 13 is for example constituted by a deposition of uniform thickness of SiO ₂ and TiO ₂ optionally modified to have anti-reflection properties. The film 13 also allows one hand to stabilize the nanofissures 11 in time, on the other hand to make the electrodes even less visible by filling the spaces between the nanofissures.

The Figures 7 to 11 show on examples how to adjust the characteristics of UV radiation. For this, three identical samples were taken comprising an intermediate layer having a thickness of 20 μm onto which a 70 nm thick ITO film was deposited and a surface of 3 × 4 mm was illuminated with an excimer laser. at 308 nm long pulses with 20 pulses at 5 Hz, varying the fluence.

The diagram shown in figure 7 corresponds to an assembly for measuring the electrical characteristics of the samples in the illuminated area. A generator 17 delivers a sinusoidal voltage of 1.77 V to a circuit comprising in series a resistor 19 calibrated between 2.2 k Ω and 570 k Ω and a portion of the sample 23, which makes it possible to deduce current values. between 0.7 m A and 0.2 μ A by measuring with a voltameter 21 the voltage across the resistor 19. (R _ech = (V _gen. -V) / I). The "sample portion 23" is taken between two tips 24 0.3 to 0.5 mm apart on either side of a nanofissure, as shown in FIG. figure 8 . It is also possible to use a loop-shaped end (not shown), that is to say to have a softened contact to prevent deterioration of the ITO film by the tips.

When the sample has not undergone any UV irradiation, the resistance between tips is 180 Ω for a current flowing through the sample of 1.5 mA with a calibrated resistor of 670 Ω.

To the figure 8 the observed image was redrawn by reflection microscopy with a magnification of about 15 times, after irradiation with a laser beam having the above characteristics and a fluence of 65 mJ / cm ² . It is observed that nonofissures are numerous. By performing the same electrical measurements as for the non-illuminated sample with the same distance between measuring points, the alternating current is no longer measurable ("0.2 μA), which means that the ITO other of the crack 11 are sufficiently electrically insulated.

This is confirmed by AFM imaging made through a nanofissure and represented in the figure 11 . It can be seen that the nanofissure has a maximum depth of 75 nm, that is to say that the base of said nanofissure penetrates very slightly into the hardcoating insulator 3 making the lower edges of the nanofissure are electrically separated by about 70 nm. It can also be seen that, at the upper part, the maximum width of the nanofissure 11 is of the order of 500 nm, that is to say a width much too small to be detected with the naked eye.

By performing the same irradiation on a second sample but with a lower fluence, namely 60 mJ / cm ² , fissures are also obtained, as shown in FIG. figure 9 , but with a small variation in electrical characteristics. With an initial resistance of 670 Q, a resistance between 800 Ω peaks and a current of 1.19 mA is observed, meaning that there is still a significant conductivity at the crack. By AFM imaging (not shown) it is indeed possible to determine that the maximum depth of the crack is 66 nm, that is to say that there remains an electrical conduction junction at the base of the crack.

Conversely, referring to the figure 10 it can be seen that by increasing the fluence from 65 mJ / cm ² to 70 mJ / cm ² , zones 22 are formed in which the ITO film is torn off to a width sufficient to make the zone separating the electrodes visible to the naked eye. The electrical conductivity is obviously interrupted, but it is then necessary to carry out a complementary manufacturing step to obtain an optical compensation, for example according to the method proposed in the application EP No. 1,457,865 already mentioned.

It is obvious that one skilled in the art can, depending on a part of the nature of the TCO film, or even that of the intermediate layer and their respective thicknesses, define the characteristics of the UV radiation depending on the source laser used to be between a lower limit where the interruption of electrical conductivity is insufficient and an upper limit where there is TCO pulling.

Thus, under the same measurement conditions as those described with reference to the figure 8 obtain the same results concerning the electrical conductivity when the irradiated zone has a surface area of 1 x 4 mm ² with a fluence of 85 mJ / cm ² .

Using a laser at 248 nm, short pulses, one also obtains the result corresponding to the figure 8 with a sample of 2 x 8 mm ² , with 50 pulses at 5 Hz and a fluence of 50 mJ / cm ² .

Depending on the laser source used which is not limited to an eximer laser, the skilled person can therefore easily, by some preliminary tests, determine the optimal conditions for causing nanofissures without removal of material, but so sufficient to interrupt the electrical conductivity between electrodes.

Claims (16)

1. Transparent substrate with invisible electrodes including a transparent support (1) on which there is deposited a transparent conductive film (5),
   characterized in that fissures (11) whose maximum width is less than the human acuteness of vision are incorporated in the transparent conductive film (5) in order to define non-conductive spaces (9) appropriate to structure in a non visible manner in said transparent conductive film electrodes (7) and their contact zones (15).
2. Substrate according to claim 1, characterized in that the transparent conductive film (5) is a transparent conductive oxide (TCO), selected from the group comprising tin and indium oxide (ITO), In₂O₃ and SnO₂ doped with Sb.
3. Substrate according to claim 2, characterized in that the conductive film (5) is an ITO film having a thickness comprised between 50 and 100 nm, preferably between 65 and 75 nm.
4. Substrate according to claim 1, characterized in that the transparent conductive film (5) is a doped conductive polymer with conjugated double bonds selected from among a polyacetylene and polyanilines.
5. Substrate according to any of the preceding claims, characterized in that an intermediate layer (3) made of a transparent hard non-conductive material or hardcoating is inserted between the support (1) and the transparent conductive film (5).
6. Substrate according to claim 5, characterized in that the intermediate layer (3) is formed of a resin incorporating SiO₂ and having a thickness at least equal to 20 µm.
7. Substrate according to any of the preceding claims, characterized in that the majority of the fissures (11) pass through the entire conductive film.
8. Substrate according to any of the preceding claims, characterized in that the support (1) is made of a material selected from among polymethylene methacrylate (PMMA) and polycarbonate (PC).
9. Substrate according to any one of the preceding claims, characterized in that the electrodes (7) and the non-conductive spaces (9) are further coated with a protective film (13) also able to have anti-reflective properties, said protective film (13) not covering the contact zones (15) of the electrodes (7).
10. Substrate according to any of the preceding claims, characterized in that it forms a touch-type control screen for an electronic apparatus in which it is integrated.
11. Substrate according to any of claims 1 to 9, characterized in that it forms at least one closing plate for a liquid crystal display cell or a photovoltaic cell for an electronic apparatus.
12. Method of manufacturing a transparent substrate with invisible electrodes including a transparent support (1) on which there is deposited a transparent conductive film (5) wherein electrodes (7) are structured with contours separated by non-conductive spaces (9), by UV radiation by means of a radiation source (14),
    characterized in that it comprises of the following steps:

    - placing the substrate, formed of the support (1) and the transparent conductive film (5) possibly deposited on an intermediate layer (3) made of a transparent hard non-conductive material, in a sealed enclosed space (2) having a gaseous fluid supply inlet (4) and a pump outlet (6);

    - inserting, between the UV radiation source (14) and the substrate, a mask (10) including windows (12) transparent to UV radiation, said windows corresponding to the non-conductive spaces (9), and

    - adjusting, as a function of the choice of materials used for the substrate and the emitting source (14), the UV radiation features to cause fissures to be created in the transparent conductive film (5) whose maximum width is less than the human acuteness of vision in the radiated zone.
13. Method according to claim 12, characterized in that it includes an additional step of depositing a conductive film (13), which may be anti-reflective, from a precursor gas with the same UV source (14), but replacing the mask (10) used by another mask corresponding to the desired useful surface of the transparent substrate, while leaving the contact zones (15) of the electrodes (7) visible.
14. Method according to claim 12, characterized in that the transparent conductive film (5) is a transparent conductive oxide (TOC) selected from the group comprising tin and indium oxide (ITO), In₂O₃ and SnO₂ doped with Sb.
15. Method according to claim 12, characterized in that the transparent conductive film (5) is a doped conductive polymer selected from among a polyacetylene and polyanilines.
16. Method according to claim 12, characterized in that the source (14) is formed by an excimer laser selected from among XeF long pulse lasers and KrF short pulse lasers.

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